Cooling system works without electricity

Stanford University technologists have succeeded in cooling water without electricity. This is achieved by sending excess heat into space, using specialized optical surfaces.

Scientists have developed a cooling method capable of ejecting excess heat out of the atmosphere in the form of infrared rays.

Packard Electrical Engineering at Stanford University

The special optical surfaces are regarded as a major step toward applying this new technology to air conditioning and refrigeration, offering businesses a lower cost means of using cooling systems. There is also an environmental advantage with the new technology, in terms of reducing energy consumption and carbon emissions. The technology, which was devised by Professor Shanhui Fan and his research team, exists as a working model: on the roof of the Packard Electrical Engineering Building at Stanford University. The roof works as a system of optical surfaces that can cool flowing water to a temperature below that of the surrounding air. The entire cooling process is, remarkably, done without the use of electricity. Air conditioning and refrigeration systems consume 17 percent of electricity generated worldwide and account for 10 percent of global greenhouse gas emissions. The new technology would significantly reduce these measures.

In an interview, one of the researchers, Aaswath Raman said that the working model "provides for the first time a high-fidelity technology demonstration of how you can use radiative sky cooling to passively cool a fluid and, in doing so, connect it with cooling systems to save electricity."

The basis of the technology is where all objects emit infrared thermal radiation, most wavelengths are absorbed by the atmosphere. This limits how cool a given object can become. To overcome this the researchers developed the method of radiative cooling. This process tweaks the wavelengths of the emitted radiation to sit only within the narrow band (which falls between 8 and 13 micrometres) that is able to escape the atmosphere. Through this application, an object is allowed to cool to below the ambient air temperature.

With the test panels, the scientists discovered that when water is moving at a relatively fast rate, the panels were able to consistently reduce the temperature of the water 3 to 5 degrees Celsius below ambient air temperature. This was demonstrated over a period of three days. This translates to a 21 percent reduction in the electricity used to cool a typical building.

The technology is not simply an academic exercise for the process has been commercialized and a start-up venture launched called SkyCool Systems. Meanwhile, the academic text has been published in the journal Nature Energy with the research paper titled "Sub-ambient non-evaporative fluid cooling with the sky."